The present exemplary embodiment relates to a scheduling system. It finds particular application in conjunction with scheduling print jobs for optimizing run cost and improving reliability for multi-engine printing systems and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Electronic printing systems typically employ a scanner for scanning image-bearing documents and conversion electronics for converting the image to image signals or pixels. The signals are stored and are read out successively to a printer for formation of the images on photoconductive output media such as a photoreceptor. When a single or multiple print job is to be printed, a process known as “load balancing” is commonly implemented. Load balancing is the ability of a printer system to complete a printing job(s) using all the available print engines to complete the print job(s) in the least amount of time. A control system associated with the image output terminal (IOT) of the machine identifies that magnitude of the print job that has been scheduled and determines the number of print pages per print engine necessary to complete the print job. In some cases, the control system will enable several, or all, of the print engines to begin printing simultaneously in order to complete the job in the least amount of time while engaging the maximum number of resources (print engines) available.
U.S. Pat. No. 6,618,167 to Shah, the disclosure of which is incorporated herein by reference, provides a scheduling scheme to improve the productivity of printers, particularly color printers. The scheduling scheme accounts for difference in the rasterization execution time of some print jobs.
U.S. Pat. No. 5,095,369 to Ortiz, et al., incorporated herein by reference, discloses a method for enhancing productivity in an electronic printer incorporating finishing activities and operating in a job streaming mode. Printing and collating of sets of original scanned documents are controlled so that collated sets are successively presented by the printer to the finisher nearly coincident with conclusion of the finishing activity being accomplished for a current job. The system uses a predictive algorithm which is used to increase reliability of printer components by cycling down the printer between jobs in situations where the finishing activity for a current job requires an extraordinarily long time to complete compared with the cycle down/cycle up time of the printer.
Printing systems now being developed may employ multiple print engines for black, process (or full) color, and custom color (single color or monochrome) printing of selected pages within a print job. The following references, the disclosures of which are incorporated by reference in their entireties, variously relating to what have been variously called “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different printers, such as separate printing of the color and monochrome pages), and “output merger” or “interposer” systems: U.S. Pat. No. 5,568,246 to Keller, et al., U.S. Pat. No. 4,587,532 to Asano, U.S. Pat. No. 5,570,172 to Acquaviva, U.S. Pat. No. 5,596,416 to Barry, et al.; U.S. Pat. No. 5,995,721 to Rourke et al; U.S. Pat. No. 4,579,446 to Fujino; U.S. Pat. No. 5,389,969 to Soler, et al.; a 1991 “Xerox Disclosure Journal” publication of November-December 1991, Vol. 16, No. 6, pp. 381-383 by Paul F. Morgan; and a Xerox Aug. 3, 2001 “TAX” publication product announcement entitled “Cluster Printing Solution Announced.”
Intermittent use of xerographic printers, characterized by relatively frequent on-off cycles has been shown, statistically, to lead to higher run cost (cost per printed page) and lower reliability. As with the operation of a car, startup and stopping are much more stressful than constant operation. Using a printer casually for relatively short jobs is much more stressful, as measured by maintenance costs per page, than running the same printer more continuously.
Several multi-engine architectures have been proposed and implemented. One of the issues with multi-engine systems is that the additional cycle up/down stress due to shorter run lengths per printer can have a detrimental effect on the life of the photoreceptor (PR) or other elements. For example, if a 30 sheet job is run on a single engine system, the system will cycle up, print the job and then cycle down. The impact of the cycle up/down time on component life will be relatively small. However, if the same job is run on a two engine system, with each engine cycling up, printing roughly 15 sheets, and then cycling down, the relative impact of the cycle up/down time on the overall component life will be larger. This affect will be different on different marking engines depending upon their cycle up/down time. This affect will not be a significant factor if job queuing is used to keep multiple engine printing systems running for long periods of time, however it is desirable to identify a method to reduce the impact of this affect when shorter jobs are run.